A Texas man's quest to find out what happened to his sister and two other girls who disappeared more than four decades ago may depend on what he finds at the bottom of a Fort Worth-area lake.

Rusty Arnold was 11 when his 17-year-old sister, Rachel Arnold Trlica, went Christmas shopping on Dec. 23, 1974 with her 14-year-old friend, Lisa Renee Wilson, and 9-year-old Julie Ann Moseley. None of the girls were seen again.

"We're never going to give up. Never going to go away. Somebody out there knows what happened to these girls,” Arnold told FOX4 on Friday. “They're not going to go quietly. They’re gonna go kicking and screaming if someone took them by force. I think they went with somebody they knew and they trusted."

Arnold has continued his own search over the years, creating a website in hopes of finding clues and conducting searches at various sites across Texas. That's led him to three submerged cars in Benbrook Lake, located southwest of Fort Worth.

Divers will extract three submerged cars from Benbrook Lake in September in hopes of finding some clues related to the three girls.
(Google Street View)

He told the Star-Telegram his group of volunteers are interested in one vehicle in particular, because he believes one of the cars belongs to a "person of interest" who knew the girls.

“At the same time the girls went missing, we believe the vehicle he was driving also disappeared,” Arnold told the newspaper. “We sat around coming up with theories, and we discovered that the person of interest lived within five miles of Benbrook Lake at the time. It’s a hunch.”

Arnold, who has not disclosed in interviews how he came to focus on the three vehicles, said a friend used sonar and came across the submerged vehicles.

A group of divers plan to raise the three vehicles out of the lake next month, and search for any clues related to the disappearance of the girls.

Arnold told FOX4 that police have told him there's not enough evidence to justify their presence, which is why he helped raise $10,000 from donations to pay North Teas Marine Salvage & Recovery to go into the murky waters. The group conducted a practice dive at a different lake on Friday to prepare them for what to expect in September.

On the heels of solving a 30-year-old Fort Wayne murder case using DNA testing, investigators who cracked the case are now assisting Delphi detectives in trying to find man suspected of killing two Indiana girls.